Traditionally, psychology has been the study of two populations: university freshmen and white rats.

From the essay "Toward a Theory of Moral Development," published in the anthology The Next Fifty Years: Science in the First Half of the Twenty-First Century, edited by John Brockman

It’s relevant that people whose polling places are schools are more likely to vote for sales taxes that will fund education. Or that judges become more likely to deny parole the longer they go without a break. Or that people serve themselves more food when using a large plate. Such effects, even when they’re small, can make a practical difference, especially when they influence votes and justice and health. But their existence doesn’t undermine the idea of a rational and deliberative self. To think otherwise would be like concluding that because salt adds flavor to food, nothing else does.